Helicobacter

Helicobacter is a genus of gram-negative bacteria possessing a characteristic helical shape. They were initially considered to be members of the genus Campylobacter, but in 1989, Goodwin et al. published sufficient reasons to justify the new genus name Helicobacter.<ref>Template:Cite journal</ref> The genus Helicobacter contains about 35 species.<ref name= BoyanovaL>Template:Cite book</ref><ref>Template:Cite journal</ref><ref name= YamaokaY>Template:Cite book</ref>

Some species have been found living in the lining of the upper gastrointestinal tract, as well as the liver of mammals and some birds.<ref>Template:Cite book</ref> The most widely known species of the genus is H. pylori, which infects up to 50% of the human population.<ref name="YamaokaY"/> It also serves as the type species of the genus. Some strains of this bacterium are pathogenic to humans, as they are strongly associated with peptic ulcers, chronic gastritis, duodenitis, and stomach cancer.

Helicobacter species are able to thrive in the very acidic mammalian stomach by producing large quantities of the enzyme urease, which locally raises the pH from about 2 to a more biocompatible range of 6 to 7.<ref>Template:Cite journal</ref> Bacteria belonging to this genus are usually susceptible to antibiotics such as penicillin, are microaerophilic (optimal oxygen concentration between 5 and 14%) capnophiles, and are fast-moving with their flagella.<ref>Template:Cite journal</ref><ref name= Rustetal>Template:Cite book</ref>

Molecular signatures

Comparative genomic analysis has led to the identification of 11 proteins that are uniquely found in the Helicobacteraceae. Of these proteins, seven are found in all species of the family, while the remaining four are not found in any Helicobacter strains and are unique to Wollinella. Additionally, a rare genetic event has led to the fusion of the rpoB and rpoC genes in this family, which is characteristic of them.<ref>Template:Cite journal</ref>

Non-H. pylori species

Recently, new gastric (H. suis and H. baculiformis) and enterohepatic (H. equorum) species have been reported. H. pylori is of primary importance for medicine, but non-H. pylori species, which naturally inhabit mammals (except humans) and birds, have been detected in human clinical specimens. These encompass two (gastric and enterohepatic) groups, showing different organ specificity. Importantly, some species, such as H. hepaticus, H. mustelae, and probably H. bilis, exhibit carcinogenic potential in animals. They harbour many virulence genes and may cause diseases not only in animals, but also in humans. Gastric species such as H. suis (most often), H. felis, H. bizzozeronii, and H. salomonis have been associated with chronic gastritis and peptic ulcers in humans, and importantly, with higher risk for MALT lymphoma compared to H. pylori.

Enterohepatic species e.g., H. hepaticus, H. bilis, and H. ganmani, have been detected by PCR, but still are not isolated from specimens of patients with hepatobiliary diseases. Moreover, they may be associated with Crohn's disease and ulcerative colitis. The significance of avian helicobacters (H. pullorum, H. anseris, and H. brantae) also has been evaluated extensively. H. cinaedi and H. canis can cause severe infections, mostly in immunocompromised patients with animal exposure. Briefly, the role of these species in veterinary and human medicine is increasingly recognised. Several other topics such as isolation of still uncultured species, antibiotic resistance, and treatment regimens for infections and pathogenesis and possible carcinogenesis in humans should be evaluated.<ref name="BoyanovaL" />

H. heilmannii sensu lato

Helicobacter heilmannii sensu lato (i.e. H. heilmanni s.l.) is a grouping of non-H. pylori Helicobacter species that take as part of their definition a similarity to H. pylori in being associated with the development of stomach inflammation, stomach ulcers,<ref name="pmid25548476">Template:Cite journal</ref> duodenum ulcers,<ref name="pmid22653899">Template:Cite journal</ref> stomach cancers that are not lymphomas, and extranodal marginal B cell lymphoma of the stomach in humans and animals.<ref name="pmid25548476"/> Most clinical studies have not identified the exact species of H. heilmanii associated with these diseases, so designated these species as H. heilmanni s.l. However, investigative studies have identified these species in some patients with the cited H. heilmanni s.l.-associated upper gastrointestinal tract diseases. The H. heilmani species identified to date in the stomachs of humans with the cited upper gastrointestinal tract diseases are: Helicobacter bizzozeronii, Helicobacter felis, Helicobacter salomonis, Helicobacter suis, and Helicobacter heilmannii s.s.<ref name="pmid25548476"/> It is important to recognize the association of H. heilmannii sensu lato with these upper gastrointestinal tract diseases, particularly extranodal marginal zone lymphoma of the stomach, because some of them have been successfully treated using antibiotic-based drug regimens directed against the instigating H. heilmannii sensu lato species.<ref name="pmid31486233">Template:Cite journal</ref> The H. heilmanni s.l.-associated human diseases appear to be acquired from pets and farm animals, so are considered to be zoonotic diseases.<ref name="pmid25548476"/>

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)<ref name=LPSN>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and National Center for Biotechnology Information (NCBI)<ref name=NCBI>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

16S rRNA based LTP_10_2024<ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>	120 marker proteins based GTDB 09-RS220<ref name="about">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref name="tree">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref><ref name="taxon_history">{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>

Species incertae sedis:

• "Ca. H. bovis" De Groote et al. 1999
• "H. callitrichis" Won et al. 2007
• "Ca. H. cebus" Gueneau de Novoa et al. 2001a
• "H. higonensis" Tomida et al. 2024
• "H. muricola" Won et al. 2002
• "H. peregrinus" Coldham et al. 2004
• "H. suncus" Goto et al. 1998
• "H. tursiopsae" Gueneau de Novoa et al. 2001b
• "H. vulpecula" Coldham et al. 2004

See also

• List of bacterial orders
• List of bacteria genera

External links

• Helicobacter genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
• List of species in Helicobacter, with links to sequence information
• Helicobacter at BacDive - the Bacterial Diversity Metadatabase